Secondary Adrenal Insufficiency
(See also Overview of Adrenal Function.)
Secondary adrenal insufficiency may occur in
Inadequate ACTH can also result from failure of the hypothalamus to stimulate pituitary ACTH production, which is sometimes called tertiary adrenal insufficiency.
Panhypopituitarism may occur secondary to pituitary tumors, various other tumors, granulomas, and, rarely, infection or trauma that destroys pituitary tissue. In younger people, panhypopituitarism may occur secondary to a craniopharyngioma.
Patients receiving corticosteroids for > 4 weeks may have insufficient ACTH secretion during metabolic stress to stimulate the adrenals to produce adequate quantities of corticosteroids, or they may have atrophic adrenals that are unresponsive to ACTH. These problems may persist for up to 1 year after corticosteroid treatment is stopped.
Symptoms and signs are similar to those of Addison disease and include fatigue, weakness, weight loss, nausea, vomiting, and diarrhea. Differentiating clinical or general laboratory features include the absence of hyperpigmentation and relatively normal electrolyte and BUN (blood urea nitrogen) levels; hyponatremia, if it occurs, is usually dilutional.
Patients with panhypopituitarism have depressed thyroid and gonadal function and hypoglycemia. Coma may supervene when symptomatic secondary adrenal insufficiency occurs. Adrenal crisis is especially likely if a patient is treated for a single endocrine gland problem, particularly with thyroxine, without hydrocortisone replacement.
Tests to differentiate primary and secondary adrenal insufficiency are discussed under Addison disease. Patients with confirmed secondary adrenal insufficiency (see table Confirmatory Serum Testing for Secondary Adrenal Insufficiency) should have CT or MRI of the brain to rule out a pituitary tumor or pituitary atrophy.
Confirmatory Serum Testing for Secondary Adrenal Insufficiency
Adequacy of the hypothalamic-pituitary-adrenal axis during tapering or after stopping long-term corticosteroid treatment can be determined by injecting cosyntropin 250 mcg IV or IM. After 30 minutes, serum cortisol should be > 20 mcg/dL (> 552 nmol/L); specific levels vary somewhat depending on the laboratory assay in use. An insulin stress test to induce hypoglycemia and a rise in cortisol is the standard for testing integrity of the hypothalamic-pituitary-adrenal axis in many centers but careful monitoring is required to avoid severe prolonged hypoglycemia.
The corticotropin-releasing hormone (CRH) test can be used to distinguish between hypothalamic and pituitary causes but is rarely used in clinical practice. After administration of CRH 100 mcg (or 1 mcg/kg) IV, the normal response is a rise of plasma ACTH of 30 to 40 pg/mL (6.6 to 8.8 pmol/L); patients with pituitary failure do not respond, whereas those with hypothalamic disease usually do.
Glucocorticoid replacement is similar to that described for Addison disease. Each case varies regarding the type and degree of specific hormone deficiencies. Normally, cortisol is secreted maximally in the early morning and minimally at night. Thus, hydrocortisone (identical to cortisol) is given in 2 or 3 divided doses with a typical total daily dose of 15 to 30 mg. One regimen gives half the total in the morning, and the remaining half split between lunchtime and early evening (eg, 10 mg, 5 mg, 5 mg). Others give two-thirds in the morning and one-third in the evening. Doses immediately before bed should generally be avoided because they may cause insomnia. Alternatively, prednisone 4 to 5 mg orally in the morning and possibly an additional 2.5 mg orally in the evening may be used. During acute febrile illness or after trauma, patients receiving corticosteroids for nonendocrine disorders may require supplemental doses to augment their endogenous hydrocortisone production.
Fludrocortisone is not required because the intact adrenals produce aldosterone.
In panhypopituitarism, other pituitary deficiencies should be treated appropriately.
Secondary adrenal insufficiency involves adrenocorticotropic hormone (ACTH) deficiency due to pituitary or, less often, hypothalamic causes (including suppression by long-term corticosteroid use).
Other endocrine deficiencies (eg, hypothyroidism, growth hormone deficiency) may coexist.
Unlike in Addison disease, hyperpigmentation does not occur and serum sodium and potassium levels are relatively normal.
ACTH and cortisol levels both are low.
Glucocorticoid replacement is required, but mineralocorticoids (eg, fludrocortisone) are not necessary.
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